The present invention relates to a coil assembly such as a common-mode choke coil.
Recently, high-frequency transmission signals are becoming commonplace in such interface standards as the USB 2.0 standard, a high-speed interface for personal computers and the like, and the HTMI standard, a digital video and audio input/output interface for digital video and the like. In accordance with using high-frequency transmission signals, these standards employ a differential transmission method that reduces the effects of noise interference and signal error by transmitting signals in opposite phase along two conducting wires.
In reality, however, common-mode noise currents are often generated due to differences in the communication properties of the two conducting wires, for example. In such a case, the wires may act as antennas and radiate noise. Japanese patent application publication No. 2003-133148 proposes one common-mode choke coil for reducing this noise.
Further, in interfaces employing high-frequency transmission signals, in addition to inductance, the line-to-line capacitance of the common-mode choke coils remarkably influences the characteristic impedance of the coils.